The present invention relates to coated cutting tools. It especially relates to those coated cutting tools having a refractory coating bonded to a cemented tungsten carbide based substrate.
In the past, a variety of coated and uncoated cemented carbide indexable cutting inserts have been used to mill cast irons under wet conditions. Various uncoated cemented carbide grades have excellent thermal shock resistance in wet milling of cast irons, but because they lack a refractory coating they have relatively low wear resistance. Refractory CVD (chemical vapor deposited) alumina and titanium carbide coated cemented carbide grades have relatively high wear resistance but because of the cracks in their coatings they have a susceptibility to thermal shock and chipping during wet milling of cast irons.
Refractory PVD (physical vapor deposited) coated cemented carbide grades have better chipping resistance than that of refractory coated CVD cemented carbide grades. However refractory PVD alumina and titanium carbide coated cemented carbide grades are not commercially available. The available PVD titanium nitride and titanium carbonitride coated cemented carbide grades have a wear resistance in between that of the refractory CVD alumina and titanium carbide coated grades and uncoated grades.
From the above, it can be seen that there is a need for a refractory coated cemented carbide grade having a combination of wear resistance, thermal shock resistance and chipping resistance during the wet milling of cast irons.